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Wednesday, July 22, 2009

Later this morning, Io's trailing hemisphere will experience a total solar eclipse when Ganymede passes between Io and the Sun. The eclipse runs roughly from 13:34 to 13:39 UTC (14:08-14:14 UTC as seen from Earth). The video below was created in Celestia and shows the eclipse both from above Io, showing the shadow of Ganymede cross Io's surface, and from the surface of Io, showing Ganymede pass in front of the Sun.

Computer Animation of the total eclipse of the Sun by Jupiter's moon Ganymede over the trailing hemisphere of Io on July 22, 2009. First half shows a view from 4500 miles above Io's trailing hemisphere. Second half zooms in on the sun from an unnamed volcanic pit showing the total eclipse. The animation runs from 13:30 to 13:40 UTC on July 22, 2009.

EDIT 07/22/2009 10:06 AM: Fixed the title of the article, changing Jupiter to Ganymede. Obviously, a Jupiter eclipse is nothing special. A Ganymede one is.

EDIT 07/20/2009 11:33 PM: Looks like the image from Keck II in the New Scientist article is a bit of a double exposure, making it look like multiple impact sites.

In case you missed it, an hour ago I posted some of my thoughts on this, the 40th Anniversary of the Apollo 11 landing. Don't forget to post a comment there about when you think the first humans will land on Io (never is a possible answer, but not one I necessarily agree with).

40 years ago today, two astronauts from a small, liquid water-rich planet called Earth made their first steps into the new frontier, landing on that planet's only natural satellite. These first steps were seen by people around the world, and people from around the world looked on with pride, regardless of nationality, creed, or race.

Today, humanity still explores space, but it has been 37 years since we last traveled beyond low-Earth orbit and gone to another world. We have ceded the role of explorer to our robots. This is not to say that this entirely bad. People from around the world still marvel in awe at the images returned from the Mars rovers, still going strong well past their warranty with the only thing keeping them back is the occasional tall dune or patch of soft soil, the Cassini spacecraft, orbiting Saturn and returning incredible photos and data about that world and its many moons, or the Lunar Reconnaissance Orbiter, which returned incredible photos of the hardware the Apollo astronauts left behind on the Moon just last week. While it has been a great privilege to get a chance to work on the data that these robot explorers send back, I still feel that humanity has retreated in its quest for space.

There has always been a conflict, budget-wise, between manned and unmanned exploration of space, competing for money in the narrow budgets of the various national or European space agencies and flame wars on web forums dedicated to space exploration. The topic is often so toxic that it is even banned from one of the forums I moderate, Unmannedspaceflight.com. I feel that one can't necessarily live without the other. Without a healthy manned spaceflight program, the pressure to fund a healthy unnamed one will be lower for the powers that be. We are already seeing budgets that are getting tighter for the space science division at NASA, creating potential funding problem for projects like the Europa/Jupiter System Mission. Manned spaceflight gives unmanned missions an additional purpose, to scout and map places in the solar system that we may send people to in the next few generations, or to explore places that humans will probably never visit in person (like Venus). They can provide additional infrastructure for manned mission, such as acting as communication relays. In the end, I feel that without a healthy manned spaceflight program, we can kiss the current unmanned program goodbye, ceding such a program to the Europeans or the Chinese. While we may still fund an unmanned program, it would look much more like the European one. Such a program would only allow for limited funding for outer solar system missions.

We should go back to the Moon. We should go to Mars with people. Given how much and how often Mars Sample Return has been delayed, we might as well go with a manned mission at this rate. Most critically, we must NOT treat landing on these worlds as the goal. That was the #1 mistake of the Apollo program. By treating the landing as the goal, everything else, like science, additional landings, (semi-)permanent settlement, seemed pointless and a waste of money. Why continue to send people if the goal was just to land there, take pictures, and go home. The Moon is not Disneyland. It isn't Mount Rushmore. The Moon and the Solar System in general is more like the Old West. Neil Armstrong and Buzz Aldrin were more akin to 20th Century versions of Lewis and Clark. They didn't cross a finish line; they opened up a frontier. But because landing was seen as THE goal, the way to beat the Russians, we lost that frontier. If we want it back, we need to start trotting out phrases like "Manifest Destiny" and stop think that we are going to spend a bunch of money to send people to the solar system equivalent of taking pictures with Mickey. It worked in the mid-19th Century for the United States, maybe it will work again for the world.

Kim Stanley Robinson, author of "Red Mars," "Blue Mars," and "Green Mars," has a great editorial in yesterday's Washington Post about how one good reason for permanent settlement on Mars and beyond is to reduce the environmental strain of the human population on the resources of Earth, and he has a good point. He also states that space exploration could be helpful driver for discovering solutions to climate change. Personally, I am pretty sure that Earth's environmental state will be the driving force behind colonization, though not as Robinson envisions, colonizing only "if Earth is healthy." As environmental regulations for extracting energy and other resources on Earth become more draconian, doing so on lifeless worlds like our Moon, Mars, the various rocks of the asteroid belt, and Io would become more profitable and/or necessary.

Finishing this post, I thought I would ask a question for all of you readers out there, given that it has been 40 years since humans first landed on our moon, when do you think humans will first land on Io? See I have to bring this post back on topic ;-) I am definitely interested in hear all of your responses. Just post a comment to this post!

Hopefully more observations will be acquired over the next few days to help confirm this discovery, but it looks quite plausible to me :)

The image at left was captured by Anthony Wesley on 19th July 2009 at 1554UTC from Murrumbateman Australia. The south pole is up, north pole down. The impact site is near the central meridian about an eighth of the way down.

EDIT 07/19/2009 9:23 PM: Wesley's website has been slashdotted so he has mirrored the page to another server. So if you are having trouble accessing the link above, check out http://jupiter.samba.org/

Tuesday, July 14, 2009

Tomorrow brings Io's most interesting eclipse this mutual event season as most of Io's trailing hemisphere (51° West-231° West) is plunged into darkness by Jupiter's largest moon, Ganymede. This is the culmination of a series of weekly eclipses by Ganymede on Io. With each weekly eclipse, the center of Ganymede's shadow appears further south on Io. Tomorrow, the center of Ganymede's shadow passes just north of Io's equator. The eclipse takes place tomorrow morning, July 15, between 10:45 and 10:50 UTC (3:45-4:50 MST) on Io. If you have a good telescope and want to try to observe this event, from Earth the penumbral shadow of Ganymede will reach Io at 11:19 UTC, totality will run from 11:21 to 11:25:28 UTC, and end of the eclipse comes at 11:27 UTC. The peak of the eclipse, as observed from Earth, comes at 11:23:14 UTC. The timing of this eclipse should make it a good observation target for observers in the western United States, western South America (like the European Southern Observatory), and Hawaii.

During the eclipse, Ganymede will appear 13' 17.2'' across in Io's sky (compared to our moon, which appears around 30' across in Earth's sky). The sun will appear 6' 19.9". Therefore, it is unlikely that the sun's corona would be seen during the eclipse except near the beginning and end. At its peak near Tol Ava Patera, the eclipse will last 1 minute and 55 seconds long.

For this eclipse, I've created a little fancier video using Celestia and Adobe Premiere. I think I am starting to get along with that latter software package...

Computer Animation of the total eclipse of the Sun by Jupiter's moon Ganymede over the trailing hemisphere of Io on July 15, 2009. First half shows a view from 4500 miles above Io's trailing hemisphere. Second half zooms in on the sun from east of Ra Patera showing the total eclipse. The animation runs from 10:40 to 10:55 UTC on July 15, 2009.

Plenty of important meetings related to the exploration of Io and the Jupiter system will be taking place this week. This includes a Europa/Jupiter System Mission Joint Science Definition Team (EJSM JSDT) meeting today, an Outer Planets Assessment Group (OPAG) meeting tomorrow, and the EJSM Instrument Workshop on Wednesday through Friday. I might be listening into the EJSM Instrument Workshop for at least some of the talks, but I haven't decided yet.

Van Kane has been keeping up with last week's Planetary Science Subcommittee and Decadal Survey Meetings. One of the key issues that seems to be coming to a head is the flat planetary science budget projected in the out years in the current budget proposal. This would cause increasing budget pressure on many projects, not only because of the lack of budget increases (resulting from the poor government revenues) and from cost overruns on some projects, including the albatross of planetary science, the Curiosity rover (née Mars Science Laboratory). According to Kane, Ed Weiler at the PSS meeting stated that there is not enough money in the Planetary Science Division budget projections to fund the Europa/Jupiter System Mission. As Kane stated in his blog, this is definitely bad news.

Celestia version 1.6 was officially released late last week. Celestia is definitely one of the space simulator, particularly thanks to its support for NAIF Spice kernel files for spacecraft and planetary body trajectories and orientations. The software also has built-in video and screenshot support, which I often take full advantage of for this blog.

Thursday, July 9, 2009

Thirty years ago today, on July 9, 1979, the Voyager 2 spacecraft encountered Jupiter from a distance of 650,000 kilometers about its cloudtops, marking the second Voyager project flyby of the planet. The encounter provided an opportunity to see the anti-Jupiter hemispheres of Ganymede and Callisto, to monitor changes on Jupiter and Io since the Voyager 1 encounter four months earlier, and to observe Europa up close for the first time.

Back in March, we took an extensive look at the Voyager 1 encounter with Jupiter and Io. The Voyager 1 flyby provided a revolution in our understanding of the giant planet and turned the four Galilean satellites from mere points of light we were only beginning to understand into four separate worlds, each with their own unique geologies. In particular, during the Voyager 1 encounter, active volcanism was observed on Io as well as a narrow ring around Jupiter.

For Io, the second Voyager encounter did not provide the same revolution in our understanding of that world; the clear star of the July 9 encounter was the cracked world of Europa. While Voyager 1 flew within 20,000 kilometers of Io on March 5, 1979, Voyager 2's trajectory kept the spacecraft outside Europa's orbit and, with Io on the other side of Jupiter during closest approach, Voyager 2 never came close than 1,128,000 kilometers of Io. However, the discovery of active volcanism on Io by Voyager 1 necessitated a change in the schedule of observations for the second encounter, including a 8-hour long sequence of images of a narrowing crescent Io as Voyager 2 receded from Jupiter. This prolonged observation sequence allows Voyager 2 to monitor volcanic plumes along Io's limb, including those at Amirani, Maui, and Loki. From observations such as these, Voyager 2 found that most of the plumes first observed by Voyager 1 were still active during the July 1979 encounter. Only Pele appeared to have shut down, though later observations by Hubble, Galileo, and other spacecraft seem to suggest that the Pele plume is intermittently active. Volund was not observed near the limb of Io during the Voyager 2 encounter, so it could not be determined if that plume was still active.

Earlier, Voyager 2 had observed Io while it was more illuminated by the Sun, like the image at left. The goal of these observation was to search for surface changes on Io as the result of volcanic activity between the two Voyager encounters. Among the changes observed were two new plume deposits surrounding Surt (probably active during a short, intense eruption in June 1979, but Surt was not viewed near the limb by Voyager 2 to see if it was still active) and Aten Patera. The presence of these changes from large plumes but without the observation of the plumes associated with them have led to the conclusion that large, Pele-type plumes tend to be short-lived compared to more persistent, smaller dust plumes like at Prometheus. Additional surface changes included a larger dark area within Loki Patera, the result of overturning of more surface area of the lava lake that covers much of Loki, and a change in the shape of the Pele plume deposit, from a heart shape to an oval. Subtle changes in the shape and intensity of the Pele plume deposit were also observed by Galileo in the late 1990s and early 2000s.

Of course, Io wasn't the only world Voyager 2 observed during its encounter 30 years ago. The star of the show was Europa. Europa was poorly observed during the previous Voyager encounter so this one really provided a great leap in our understanding of this icy world. Like Ganymede, Europa's surface was dominated by tectonic structures, ridges and dark, linear bands that criss-cross the surface. Unlike Ganymede, Europa's surface was found to be quite young with very few impact craters, though enough to show that the satellite's surface was much older than Io's. Spectral measurements suggesting a water ice surface, mass estimates between that of Io and Ganymede, and youth surface age soon led to the suggest that just beneath Europa's ice shell lay a liquid water ocean that today is a main focal point for exploration in the Jupiter system.

Voyager 2 never got the same amount of attention that the earlier Voyager 1 encounter did. During the same week, Skylab was slowly approaching its destruction over Australia, dampening press interest in the encounter, along with the perception that this encounter was covering similar territory as the previous one. But Voyager 2 provided an opportunity to follow up on the discoveries made by Voyager 1 by allowing for an adjustment to the observation plan, such as to monitoring Io's volcanic plumes and Jupiter's narrow ring system as Voyager 2 receded from the giant planet. Voyager 2 also allowed imaging scientists to fill out the global map of Ganymede and Callisto by observing their anti-Jovian hemisphere and providing the first close-up look of Europa. The Voyager 2 encounter unfortunately also began a 17-year gap in close-up spacecraft imaging of the Jupiter system. But Voyager 2 went on to bigger and better things, including doing followup observations of the Saturn system in August 1981 as well as our only encounters of Uranus and Neptune in 1986 and 1989, respectively.

For this post, I have posted some movies on Youtube created in Celestia showing the geometry of this encounter:

Wednesday, July 8, 2009

A new Io-related paper in the journal Icarus was posted online on Sunday titled, "Io: Heat Flow from Dark Volcanic Fields." The paper is authored by Glenn Veeder, Ashley Davies, Dennis Matson, and Torrence Johnson. The authors in this paper attempt to estimate the amount of Io's overall heat flow that is radiated from the large volcanic lava flow fields that cover a sizable portion of Io's plains, distinguishing these features from the myriad of volcanic pits, the background heat flow, and the big daddy of Ionian volcanoes, Loki Patera, which by itself radiates 5-15% of Io's total heat flow. This research was previously discussed last year on this blog when the authors of this paper submitted a print-only abstract to LPSC 2008.

Dark volcanic fields on Io are thought to consist of recently active, compound silicate lava flows that have erupted onto the plains of Io, rather than being confined within a patera (volcanic pit). Lava flows of many colors have been observed on Io, but it is the black or dark green flows that are thought to be the most recently active silicate flows. These flows tend to be lava channel (or tube)-fed, with smaller outbreaks building and growing the flow field over time. For example, if you look at Amirani above, you see "small", fresher lava flows on top of older, dark green lava. The dark green color comes from the deposition of sulfur on still-cooling, iron-rich silicate lava flows, producing iron sulfide. Brighter flows represent either older silicate flows that cooled enough for sulfur and sulfur dioxide to condense on their surfaces or sulfur-rich lava flows. Either way, bright flows were not considered in this analysis.

Veeder and his colleagues estimated the contribution of Io's dark lava flow fields to Io's total heat flow by first identifying all the dark lava flow fields visible on Io in the USGS global map and calculating the area of each flow field. Their areas were found by measuring the number of pixels below a threshold limit for each dark flow field (the threshold valuing varying with each flow field) while also removing other possible dark features such as paterae. Using this method, the authors identified 28 dark flow fields, including features such as Masubi Fluctus, Marduk Fluctus, Amirani (above left), and Prometheus (above upper right), covering slightly less than 1% of Io's surface. The authors also excluded more transient lava flows like Pillan and Thor, though sources such as these may provide a significant amount of the heat flow contribution from dark flow field heat, even if the specific sources changes over time. The authors then seem to be more focused on persistent volcanoes. The authors note a peak in the distribution of dark lava flows in the anti-Jovian hemisphere of Io, opposite Io's most powerful volcano, Loki Patera.

Next, the authors estimated the effective temperature (akin to an average nighttime temperature of each lava flow) and the total radiating power for each flow. For many of the flows, infrared data, either from the NIMS or PPR instruments on Galileo, is available, allowing for a more accurate estimate of the heat flow of each flow. For cooler flows, more accurate estimates tend to come from the PPR data since much of their heat is radiating out at longer infrared wavelengths to which PPR was more sensitive, compared to NIMS, which was more sensitive to warmer heat sources. However, for more than half of the dark lava flows examined in this study, no radiative power estimate is available. For these flows, the authors assumed an effective temperature of either 130 K or 115 K, depending on whether surface changes or other signs of recent volcanic activity have been observed.

The authors' estimate that the 28 dark flow fields they examined provide 5 x 1012 Watts to Io's global heat flow, or about 5% of Io's total heat flow. This amount is similar to Loki when it is quiescent. While their effective temperatures are cooler than many of Io's active paterae like Loki Patera or Pele, their larger surface area compared to Loki Patera (an order of magnitude greater) allows them to contribute a large amount of Io's heat flow. It should be noted that this analysis excluded brighter flows, which may provide an even greater percentage of Io's total heat flow despite having even cooler effective temperatures, a possible later research subject as Io's heat flow budget is broken down further (to an extent this has with Glenn Veeder's earlier work on the possible excess heat flow from Io's polar regions).

Sorry I haven't covered the last two eclipses (June 24 and July 1), but taking a look at today's eclipse of Io by Ganymede we see as Ganymede's shadow is now reaching further south across Io's trailing hemisphere. The eclipse will take place in about 25 minutes from the time I am typing this, but you can still see an animation of it in the Youtube video I uploaded and embedded below:

Computer Animation of the total eclipse of the Sun by Jupiter's moon Ganymede over the trailing hemisphere of Io on July 8, 2009. First half shows a view from 7,317 km above Io's northern trailing hemisphere. Second half zooms in on the sun from the floor of Loki Patera showing the total eclipse. The animation runs from 07:30 to 08:20 UTC on July 8, 2009.

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I work for the Cassini Imaging team, usually processing Titan and Enceladus images and making maps of Titan based on our images. When I am not working or studying, I'm...I forget. I watch a lot of movies I guess.